GaAs1-xNx epitaxial layers grown on (001) GaAs substrates by metal organic vapor phase epitaxy, with x ranging from 0.01 to 0.036, were characterized by ion beam analysis. The layers thickness and quality were measured by Rutherford backscattering spectrometry (RBS) in channeling mode. The channeling results confirm that GaAs1-xNx epitaxial layers are of high crystalline quality, in agreement with high resolution x-ray diffraction and transmission electron microscopy analyses. For,the sample with x = 0.036, the results reveal a 0.7 at. % of misplaced (or highly locally strained) Ga or As atoms. More than 80% of nitrogen atoms in this layer occupy substitutional sites, as determined by the N-14(alpha,p)O-17 nuclear reaction analysis (NRA). Furthermore, RBS analyses using a 5 MeV O3+ probe beam reveal measurable departures from III-V stoichiometry near the surface, which remains unexplained. Finally, the total content of nitrogen in the layers measured both by NRA and elastic recoil detection by time-of-flight are compared with the results obtained by secondary ion mass spectrometry. (C) 2004 American Vacuum Society.